The excrement and urine from pigs are highly-contaminated wastes. As environmental preservation has become more and more important, waste treatment equipments are essential to pig raisers. By fermentation treatment, a great amount of flammable biogas is produced in the treatment process. After collecting and storing, the biogas can be brought into use as a fuel for furnaces or internal combustion engines by pig raisers for a long period of time. But, due to various inconveniences, biogas has not been broadly used in electric power generators in Taiwan. Since power resources are rare in Taiwan, especially in summer, electric power is in short supplying. On the other hand, in the summer, biogas is produced at a maximum rate (the higher the temperature, the more biogas produced). Nevertheless, biogas has not been put into full use. the more biogas produced). Nevertheless, biogas has not been put into full use.
The biogas generator commonly used in Taiwan is usually a synchronous AC generator driven by a gas engine. The generator directly supplies its load. The load is mostly inductive loads (e.g. motors). This kind of load demands 3 to 5 times the rated power, i.e. the inrush power, when it starts. For supplying such a power demand, the maximum power capacity of the biogas generator is designed to exceed the need. Consequently, the cost of capital equipments is greatly raised as the power capacity increases. Furthermore, the gas consumption and the operating cost are relatively high, due to the mismatch of the power capacity and the ordinary power demand. Besides the above mentioned shortcomings, some of the major parts are expensive including the governor and the synchronous AC generator. Summing up the above, the problems that arise in biogas power generation are briefly described as follows:
(1) There are few kinds of commercial power generators designed for biogas. The power modules now in use are normally assembled by parts of different machines. These parts are not easily available, and are difficult to operate and repair.
(2) The power capacity of the generator must be much larger than the load. But the yield of biogas is decided by the number of pigs. Therefore the capital cost is high, due to high power capacity, and operating time is short, due to high gas consumption.
(3) It is difficult to connect the generators in parallel. For a user having more than one generator, an optimized operating condition can not be achieved easily.
(4) Difficult to start and stop is another problem. The engine is started by a starting motor and batteries. Only experienced personnel can do the switching and control the AC frequency.